# significant gap between the wall and moving piston

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 August 28, 2006, 05:23 significant gap between the wall and moving piston #1 Sha Guest   Posts: n/a Hi, In my problam, There is a cylinder and a psiton that creates gaps in both sides, More precisely, There are three walls - that look like this : |_| and a rigid wall(piston) that moves in sin way up and down ,The piston is narrow in a way that two gaps are created in the left and right sides. I am only intersting in the flow inside the cylinder, The area over the piston is not intersting. I will totaly appriciate detailed explantion for the soultion of this problam. I realy dont have a clue, I read a little about dynamic mesh and i preffer not to deal with UDF(its sounds complicated) Thanks a lot in advance, Sha.

 August 28, 2006, 13:21 Re: significant gap between the wall and moving pi #2 Ahmed Guest   Posts: n/a Look the tutorial for a sliding mesh

 August 28, 2006, 15:24 Re: significant gap between the wall and moving pi #3 benjo Guest   Posts: n/a hi, i have the same problam, anyone can advice a simple way to solve this problam ?

 September 20, 2006, 06:08 how can modeling a moving wall? #4 Nikolaos Guest   Posts: n/a My model consists of a box where in the top of it and in the bottom bordering with a moving wall. between the box and the moving wall exist air. the moving wall moves in the x-axis with 10 m/sec. how can give the boundary conditions to the moving wall? please help me!!!

 September 20, 2006, 11:15 Re: how can modeling a moving wall? #5 Albert F. Guest   Posts: n/a As I know you need to specify a velocity in the wall you want. You can do this by changing a couple of things in the momentum panel of the wall: Wall motion: Moving wall Motion: Relative to adjacent wall (if adjacent cell is air for exemple) Shear Stress: here there are two options no slip or specify shear. I usually specify shear stress with 0 constant stress on both directions (X an Y) to achieve a velocity profile where the velocity is 0 near the wall. If you have defined the shape as a solid you have to impose a moving reference frame on bc panel. I don't know If I have explained it clearly, any doubt ask me for more info. Hope it helps.

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